I count 8 bipolar transistors (and not even good ones) in this "tube" op amp. Kind of defeats the whole purpose doesn't it?
Q1 to Q4 are a folded cascode stage with another cascode stage on the bottom of it before somebody inevitably ask.

I'm afraid Fred is right. The lower part is the load of the differential stage and the tubes are stealing current from the differential transistors and these transistors have their inputs connected to constant DC voltage.